Telephone system



4 Sheet-Sheet l INVENTOR ATTORNEYS.

Nov. 8, 1938. H, V055 2,135,862

TELEPHONE SYSTEM Filed March 24, 1957 4 sheets-sheet 2 FIG. 2

CONNECTOR INVENTOR. JOHN H. VOSS ATToRNEYf.

Nov. 8, 1938. .1. H. Voss TELEPHONE SYSTEM Filed Maron 24, 1957 4 Sheets-Sheet 3 a, m w l n MH. w m w N m m @E www ,A J 5 @my .,m/ .Lfi... 3m, JM im v Nom\ l am mmm 9/ :9 mm 2Q @w B l .L mi 2m@ n e am. mw

J. H. Voss 235862 TELEPHONE SYSTEM Filed March 24, 1937 4 sheets-sheet 4 Nov. 8, E938.

To LINE NIGHTALARM SWITCH EMR INVENTOR. JOHN H. Voss BYQWA, Kimm; ,JmmxJgM ATTORNEYS.

Patented Nov. 8, 1938 TELEPHONE SYSTEM John H. Voss, Downers Grove, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application March 24, 1937, Serial No. 132,687

45 Claims.

The present invention relates to telephone systems and more particularly to improvements in private branch exchange systems of the type having access over trunk lines to the lines of one or 5' more central exchanges.

There are numerous well-known types of private branch exchanges of different designs such that one or more thereof is -capable of meeting n the service requirements of practically any busi- 1'0 ness requiring such a system. In the larger systems of this type automatic equipment or local switch trains, comprising the usual traflic concentration switches and connector switches conventionally employed in larger public systems, is al- 1'5 most universally used for setting up desired connections between the various party lines included in the exchange. For the extension of connections from the private exchange lines to the central exchange, however, a'number of different gg methods have been devised. One of the best arrangements yet developed for this particular purpose is that of providing, in the branch exchange, automatic equipment in the form of connector or selector switches associated with two-way trunk lines extending between the private and central exchanges and responsive to the operation of any one of the private exchange line substation impulsing means, for setting up connections directly to the equipment of the central exchange, whereby talking loops from the private exchange lines to lines terminating in the central exchange may be established, and in routing incoming calls to the lines of the private exchange through apparatus associated with an attendants cabinet or operators station in such manner that the necessary connections are set up by the operator, following which the desired connections between the calling and called lines are completed. This arrangement possesses many advantages with respect to iiexibility in the types of service available and also may easily be adapted successfully to operate in connection with any type of central exchange equipment.

The principal disadvantage of known systems of the form just described relates to the complexity of the circuits involved and the arrangement thereof, which arrangement inherently contributes to or causes mistakes on the part of the operator at the attendants cabinet. Thus, various types of service such, for example, as the completion of calls to private exchange lines, the monitoring of established connections, the holding of calls, and the like, are usually required with this type of system, and each of these various services requires one or more operations on the part of the operator in the form of the manipulation of operator controlled key switches. Consequently, where a large volume of traffic is being handled, there is great likelihood of mistakes tending tointerfere with correct service. The more serious of these errors are brought about by the operator failing to manipulate keys at the proper time, thus, in many cases, leaving central oiiice trunk line equipment tied up when it is actually idle. The last-mentioned errors are traceable directly to the fact that key switches of the self-locking type are necessarily used in all of the prior systems of this character, which switches complete directly the necessary connections for the particular service to be rendered, and these switches, when not manipulated at the proper time during a particular operation, may put the associated repeater and trunk circuits temporarily out of use.

It is an object of the present invention, therefore, to provide a system of the character briefly described which operates in a manner such that the operations required for rendering the various types of services are extremely simple and are capable oi being performed mechanically with but little thought on the part of the operator.

It is another object of the invention to provide such a system wherein, for particular types of service, only momentary operation of nonlocking operator controlled switches is required to cause the necessary connections to be established.

It is a further and more specic object of the invention to provide an arrangement of the above character wherein, at the end of the manipulation or sequence of manipulations of the operator controlled switches, necessary to render a predetermined service, and when the` operators telephone is disconnected from all lines, the switches are all in their respective normal positions.

It is a further object of the invention to provide a system of the character stated which is operable to provide practically any type of service required and possesses the utmost simplicity with respect to circuit arrangement and the type of equipment included therein.

In general, the objects as set forth above are attained in accordance with the present invention b-y providing in a system of the form described, an operators station or attendants cabinet associated with the incoming central office trunk line and repeater circuits and having its operator controlled key switches so related to the control equipment associated with the individual trunk line repeaters that only the initiation of connections for the various required services is performed by the operator controlled keY switches, the actual setting up of theY necessary connections being carried out by means in the form of relays responsive to the operation of the key switches to predetermined positions. More particularly, one or more relays are provided, each of which is so connected as to be energized or deenergized by the momentary op-V eration of one or more of the associated key switches, following which it initiates an operation, or a sequence of operations, ultimately resulting in the appropriate connections for a particular desired service. When the service is no longer .desired or when the particular repeater being used is cleared out by disconnecting an established connection, these relays and the other equipment controlled thereby'are automatically restored to normal. Wherever possible self-restoring key switches are used in association with each of these relays, thereby eliminating the possibility of key switches being left locked in a position which will interfere with the subsequent use of the associated repeater and central oiiice trunk line. The circuit arrangement of the switches and the relays controlled thereby is such that, when all of the keys normally used by the operator in performing routine services are in their respective normal positions, the operators telephone is disconnected from all lines. More specifically, the arrangement is such that the operators telephone cannot be disconnected from all of the lines unless the keys are in their normal positions, thus providing a safeguard against mistakes due to lack of thought on the part of the operator.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specication taken in connection with the accompanying drawings in, which Figure 1 illustrates diagrammatically a system of the general type described above and Figs. 2, 3, and 4, considered together, illustrate the apparatus and improved arrangement of the circuits included in the operators station and the associated trunk line circuits.

Referring now more particularly to Figure 1 of the drawings, there is diagrammatically illustrated a one thousand line system of the general form described above which includes a central oflice or exchange ID connected b-y one or more two-way trunk lines, such as the line II, to a private exchange. The latter exchange comprises two-way trunk repeater circuits, one of which is shown schematically at I2, which circuits are individually associated with the trunk lines such as the line II, to which line are accessible the apparatus of an operators station or attend-Y ants cabinet I3 and also at least a portion of the private lines included in the private exchange. The latter lines, three of which are shown at I4, I5 and I6, extend between the subscribers substations, as shown at A, B and C, respectively, and line switches included in the line switch unit I1 and are multipled to connector switches, 'one of which is indicated at I8. Each of the connector switches is preferably of the well-known Strowger type comprising bank contacts arranged in levels, wipers, and control means arranged to translate the wipers vertically opposite any de- -sired level i'n response to the dialing of one digit and then to rotate the same into engagement with the correct set of contacts in response to l the dialing of a second digit. The line switches included in the units |'I and individually associated with each of the private lines likewise may be of any desired type although preferably they are of the plunger or rotary type having their bank contacts multipled together in groups and connected over trunk lines such as that indicated at I9 to selector switches one of which is indicated at 20, individually associated with the lines I9. rIhe selector switches may also be of any desired form although, preferably, they are of the well-known Strowger type comprising bank contacts arranged in levels and multipled in groups to different groups of lines corresponding to the groups of selector bank contact multiples, each group comprising individual lines such as that shown at 2|, extending from each selector switch bank contact multiple to the connector switches, such as the switch I8. The selector switches of the form noted also comprise wipers adapted to be translated vertically to the proper level of bank contacts in response to received impulses transmitted thereto by the dialing device of a calling sub-station, following Ywhich they are automatically rotated into contact with the first idle line such as the line 2|. One group of selector switches has at least a portion of its bank contacts connected over trunk lines as indicated at 22 to the repeaters, such as the repeater I2, associated with the trunk lines, such as the line II extending to the central exchange. With this arrangemenna party on a private exchange line may, in a well-known manner, by dialing a predetermined digit cause a connection to be established directly over one of the central office trunk lines, such as II to the central exchange. An additional, or the same group of selector switches may, if desired, have one or more contact multiples extended directly over lines, such as the line 3|, to the operators station I3 to provide secretarial or executive service for at least a portion of the private lines in the private exchange in the manner more particularly described hereinafter. In order to render the subscribers lines accessible to the central exchange trunk lines such as the line cn incoming cails from the central exchange I0, line switches are individually provided for each of these trunk lines, one of which is shown at 33', which switches have their bank contacts multipled together and extended over lines, such as the line 24, to certain of the selector switches. If desired, individual selector switches may be employed to connect the lines extending from the multipled bank contacts of the line switches, such as the switch 33', to the connector switches but, preferably, certain of the selector switches, such as the switch 20 included in the switch train between the subscribers lines and the connector switches, are used for this purpose. In order to enable the operator directly to call any desired private exchange line in the private exchange without using one of the central exchange trunk lines, there are provided means in the attendants cabinet for connecting the operators telephone to the private exchange local switch train over a line 32, a line switch 33 and lines such as the line 34 extending to one or more of the selector switches. Information trunk lines, such as that shown at 3|, may also be provided Yfor use in rendering secretarial or executive service to all or certain designated ones of the private exchange lines in the manner described in detail hereinafter. In

addition, the usual provisions are made for night service, whereby incoming calls to the private exchange are routed directly to night attendants telephones included in the private exchange.

Neglecting for the present the details of the operators station or attendants cabinet I3 and the associated central exchange trunk lines and repeaters, the system as generally described above is entirely conventional in form and its operation is well understood in the art. In brief, calls between private lines within the private exchange and calls from private lines to thecentral oflice are completed independently of the attendants cabinet and the apparatus included therein, this apparatusbeing used primarily in the extension of calls originating on lines terminating at the central exchange to lines in the private exchange and in providing the various types of service describedv hereinafter. Thus, the initiation of a call on the line I4 causes the line switch included in the unit I-I associated with this line toselect an idle trunk line such as the line I9 leading to an idle selector switch such as the switch 20; 'I'he latter switch, in response to the dialing of the first digit at the station A, selects the group of trunkv lines associated with the connector switches at which the called line terminates-and thereafter automatically selects an idle one of thisl group of trunk lines to extend the connection to the associated idle connector switch. In response to the dialing of the final two digits, the selected connector switch extends the connection to the desired called line or, in case the called line is busy, returns busy tone to the calling party.

In the event a call is to be extended from one of the lines in the private exchange to a line terminating at the central exchange, the operation is exactly the same as that described above except that the call is routed in response to the dialing of one predetermined digit, such as O, by means of one of the selector switches over one of the lines such as the line 22 to a trunk line such as the line II extending to the central exchange I0. If the apparatus included in the latter exchange is automatic, the connection as thus extended to this exchange may further be extended to the called subscribers line bydialing the properl additional digits. If, on the other hand, the exchange I 0 is manual in character, the extension of a call thereto from one of the lines in the private exchange notifies the central exchange operator by suitable signal means, who thereafter ina well-known manner extends the connection to the desired central exchange line. As described in detail hereinafter, the extension of a connection from a line in the private exchange to a line in the central exchange is entirely independent of any operation on the part of the operator at the attendants cabinet I3.

On incoming calls from the central exchange, the operator at the operators station I3 is rst signaled that a particular 'central exchange trunk line is calling in, whereupon she operates one of the key switches at the station to connect her telephone to the calling trunk line and establish a talking loop extending over the trunk line from her telephone to the central exchange. 'Ihe operation of the key switch mentioned also prepares a normally uncompleted talking loop from the operators telephone to the called private exchange line by causing the associated line switch, such as thev switch 33', to seize an idle selector switch, such as the switch 20. Following receipt of the information as to theparty in the private exchange desired by the calling party, the operator momentarily operates a second key to interrupt the established talking loop to the central exchange and to connect her telephone to the prepared loop to the called private line. In response to the operators dialing of theflrst digit, this loop is extended by means of a line switch such as the switch 33', an idle line suchas the line 24 and an associated first selector switch such as the switch 2l? over an idle line such as the line 2| to the associated connector switch, following which the talking loop between the operators telephone and the called line is completed by dialing the proper nal two digits at the operators station I3. If the called party answers, the connection between the calling and called party may be completed and the disconnection of the operators telephone from the established connection may simultaneouslyl be accomplished by the restoration of the. first operated key switch to its normal position. Hence, the operators equipment is released for use in completing other calls of a similar nature. Suitable provisionsV are also made for monitoring any desired established connection, for splitting the connection so that the operator can talk with either the called or calling party to the exclusion of the other, for holding an incoming call until a desired line in the private exchange is clear and for providing all of the other services normally required in this type of exchange.

It is pointed out that each of the lines such as 22 and 35 extending respectively to and from the associated repeater, such as the repeater I 2, are of the three conductor type and that the central exchange trunk lines, such as the liney II, are of the two conductor variety. Thus, the line 22 comprises two talking conductors 28 and 2.9 and a control conductor 30, the line 35 'comprises a pair of talking conductors 25 and 21- and a control conductor 26, and the trunk line III comprises a pair of talking conductors 23 and 24. From the foregoing general description it will be appreciated that each of the trunk lines,`

such as the line II, comprises a portion of an uncompleted talking loop extending between the operators telephone and the central exchange, that each of the lines 35- comprises a part of a normally uncompleted talking loop extending from the operators telephone to any desired line in the private exchange, and that when these two loops are connected together an extended talking loop is completed between the calling and called telephones. It will further be appreciated that the local switch train of the private exchange, comprising the line switches such as the switch 33', the selector switches such as the switch 2li and the connector switches such as the switch i8, is associated with the normally uncompleted loop extending between the operators telephone and each of the private exchange lines and that this switch train is arranged to, be responsive to operation of the impulsing or dialing device at the operators station.

Referring now to Figs. 2, 3, and 4, there are illustrated the features of the present invention as embodied in the apparatus for setting up, in the above described manner, connections betweenthe private exchange lines included inthe private eX- change and the lines extending to the central exchange I0, and more particularly as embodied in the circuits and apparatus of the repeater I2 associated with the central oicetrunk line- II, thecircuits andV apparatus of the operators-sta- III tion or attendants cabinet I3 and the connections between the various elements of these two portions of the system. It is pointed out here that the various relays involved are, for convenience in following the description, related to the numberof the ligure in which they appear, being numbered consecutively in steps of ten with the intervening numbers designating the armatures of the corresponding relays. In brief, theV portions of the system shown in detail in Figs. 2 and 3 comprise; a normally interrupted talking loop extending from the operators station to the central exchange and including the repeater windings 204 and 205 of a repeater 200 connected in series with each other across the trunk line conductors 23 and 24 through the voice current coupling condenser 206 and a resistor 201; a normally uncompleted outgoing private exchange talking loop including the repeater wind-ings 20| and 202 connected in series by means of a condenser 203 across the line conductors 2 |4 and 2| 5 and terminating at the banks of one of the selector switches such as 20; a normally uncompleted talking loop extending from the operators telephone to any one of the private exchange lines by way of the conductors 228 and 22 9, the conductors 214 and 215, the conductors 25 and 21 and the line switch 33'; a normally uncompleted talkingloop between the central exchange and any one of the private exchange lines comprising elements of the rst and third loops as described above and the conductors 216 and 211; and means comprising different groups of the plurality of relays shown and their control and controlled circuits for setting up either alone or in cooperation with certain elements of the equipment in the attendants cabinet the variety of connections necessary to a rendition of the various required services. Thus, there is provided means included in the repeater circuit and operative to set up a connection from a private line by way of the trunk line to the central exchange, which means comprises relays 2|0, 3|0 and 320 operative in the order named during such an operation, the conductors included'in the circuits controlling these relays and the conductors included in the circuits controlled thereby. Similarly, there is provided means included in this portion of the system for setting up connections to a desired private line 0n a call from the central exchange, which means comprises, in addition to an operator controlled trunk line answer and release key switch 425, a switch 428' and an impulsing device 458 at the operators station I3, relays 330, 340, 350, 360, 230, and 310, operative in theorder named during the initiation of such a connection, and relays 250, 2|0, 3|0, 320, and 260, which also operate in the order named, to complete the connection following the appropriate manipulation of the switch 425 and 426 and the impulsing device 458. In addition, there is provided a condenser 218 which is connected in series with the two halves of the line 229 for a purpose to be described hereinafter, and various other circuit elements and conductors which are speciiically referred to hereinafter.

The apparatus at the operators station shown in Fig. 4 comprises, in addition to a plurality of operator controlled switches 425, one for each of the central oice trunk lines such as Il, a night switch 424, an operator controlled local release and monitoring key switch 421, an operator controlled trunk connect and local key switch 426, a night alarm key switch 410, an information key switch 482, an operators line key switch 483, suitable indicating lamps 400, 40|, 484, and 4|0, and an operators telephone indicated generally at 500 and including all of the apparatus to the left of the terminals 465 and 466. This telephone is accessible and may be connected to the trunk line by means comprising the conductors 228 and 229. It will be understood that these conductors are multipled to armatures of additional relays such as the relay 250 individually associated with corresponding ones of other central exchange trunk lines, thereby to make the operators telephone accessible to any one of these trunk lines. In this connection it is pointed out that switches such as the switches 424, 425, and 410 are individually provided for each trunk line and that the remaining switches are common to the operators equipment, only one of each being required for the telephone 500. In addition, there is included at the operators station conductors interconnecting the contacts of the various switches, some of which extend to the control means associated with the trunk and all suitably indentied by reference characters to facilitate a description of the operation of the apparatus.

Each of the operator controlled switches 425, 426 and 421 may be of any desired commercial construction and comprises, in addition to the contact springs shown, a suitable camming element for operating the contact springs. Each switch has a normal position, corresponding to the unbiased positions of the contact springs as illustrated in the drawings, and at least one oftnormal position wherein the right or left-hand contact springs are biased into or out of engagement with their associated contacts. In addition, each of the switches is, so far as possible, constructed to be of the non-locking type such that, when released from an olf-normal position, it automatically restores to its normal position. Thus, the switch 425 automatically restores from its trunk release or right-hand off-normal position and is locked when operated to its answer or left-hand oil-normal position, the switch 426 automatically restores to normal when released from either of its two off-normal positions, and the switch 421 locks itself in an oir-normal position only when its camming element is moved to the left. The practicability of employing, whereever possible, self-restoring key switches results from the arrangement of the circuit elements in accordance with the present invention. It will be appreciated that by using such key switches mistakes on the part of the operator are minimized. v

The operators telephone or substation 500 may be of any desired type, although, preferably, is of the well-known anti-side tone, booster type, of which there are several well-known modications in the art. It comprises an operators hand set including a receiver 459 and a transmitter 460 adapted to be connected in Vcircuit for operation by the hook switch comprising associated pairs of contacts 46| and 462. Thus, when the hand set is lifted from the hook switch, the receiver terminals extend by way of the contacts 462 and a condenser 461 to opposite terminals of a winding 448 embodied in a three winding induction coil 450, the terminals of the receiver being shunted by a rectier 468, preferably of the copper oxide type, which functions to prevent current surges through the receiver during dialing and thereby to prevent receiver clicks. Connected in series with the winding 448 acrossthe line conductors 445 and 446 by way of contacts inthe impulsing device 458, the switches 426 and 421 and the hook switch is` a second winding 441. Inductively coupled to these two windings is the third winding 449 of the coil having its terminals extending to the terminals of the transmitter 460. Current is supplied to the transmitter 460 from common battery through two resistive inductors indicated at 464, the series combination of these inductors and the common battery being by-passed for audio frequency currents by a condenser 463. The impulsing device conventionally comprises impulse contact springs 452 and 453 shunted by an anti-contact-sparking circuit comprising a resistor 480 and a condenser 48I, and contact springs 454, 455 and 456, 401 for shunting the receiver 459 and the induction coil windings 441 and 448 during a dialing or impulsing operation. Since the operation of this type of substation circuit is well known in the art, a detailed explanation is deemed to be unnecessary and is omitted in the interests of simplicity.

The above described control apparatus at the operators station in conjunction with the control means associated With the trunk line II is capable, when properly operated, of providing in an improved manner practically all of the services usually required in the type of system shown. Thus, in the operation of the repeater circuit to extendra connection from one of the lines in the private exchange to the central exchange and following the seizure, at the selector switch 20, of the trunk II and its associated repeater I2 in the manner previously described, the windings of the relay 2I0 are energized over a circuit extending from ground at the lower winding of the relay 2I0, through this winding, the armature 248 of the relay 240, the conductor 208, the winding 202 of the repeater 200, the line conductor 2I5, the armature 23I of relay 230, the trunk line conductor 28, over the closed bridge across the conductors 28 and 29, the trunk line conductor 29, the armature 232 of relay 230, the line conductor 2 I4, the repeating coil winding 20|, the conductor 209, the armature 241 of relay 240 and through the upper winding of relay 2 I0 to battery. The relay 2 I0 operatesr to complete at its armature 2l I a circuit including the conductor 341 for energizing the upper winding of the relay 250 and the relay 3I0, and also to close at its armature 2I2 ground from the armature 323 of relay 320 to the negative trunk line conductor 24 over a path including the winding 204 of the repeater 200, the resistor 201 and the winding 205 of the repeater 200. The relay 2I0 also closes its armature 2I3 to the associated contact, but this operation is Without effect since the conductor 2I6, to which the; armature 2I3 is connected, is held from ground at the armature 251 of relay 250.

The energization ofthe upper winding of the relay 260 is insufficient to cause operation thereof, this relay operating only when both its windings are cumulatively energized. The eiiect of closing ground to the negative trunk line conductor 2'4 at the armature 2I2 is to operate equipment in the central oiiice, the nature of the operation depending upon the type of equipment employed therein, i. e., whether automatic or manual, as will be pointed out hereinafter. In either case ground is returned over the positive trunk line conductor 23 so that when the relay :imv operates it completes at SI5 an obvious energizing circuit for the upper winding of relay 32@ and, prepares at its armature SII a holding circuit for this relay including the lower winding thereof. In addition, the relay 310 closes at its armature 3l@ ground to the control or C conductor 2I8 which extends back through the contact 2 I9 and armature 226 of the test busy switch to the bank contacts of the connector switch or switches to prevent the repeater I2 and associated trunk line II from being seized thereat until the trunk line is released. The relay BIIB at its armature SI2 also closes ground to the motor start or ringing machine conductor 221, thereby to initiate operation of the ringing apparatus (not shown), and opens at its armature 2I3 the energizing circuit of the relay 335 normally bridged across the line conductors 23 and 24.

The application of ground to the C conductor 2I8 in the manner described above, in addition to marking the trunk line Ii as busy, causes the busy lamp 400 included in the attendants cabinet to be lighted over a circuit extending from ground over the conductor 2 I8, through the contact ZIB and armature 225 or the busy switch, the conductor M3, the armature 4I?, and contact 4I8 of the night switch 424, and through the lamp 400 to battery. The lighting of this one lamp indicates to the operator that the repeater and associated trunk line I I are in use by a party in the private exchange calling through to the central exchange.'

The relay 320 is of the well-known two-step type such that when its upper winding is enegized in the above described manner its X contacts only are closed at the armature 324. The closure of these contacts completes the previously prepared circuit for the lower winding of the relay by way of the armature SII, thereby resulting in its complete operation to complete, at its armature 322, a talking loop extending from the calling line to the central exchange and in the closure, at its armature 32I, of a multiple groundto the C conductor ZIB. Operation of the armature 322 also disconnects ground from the negative line conductor 24 at the armature 323, to interrupt the circuit of the upper winding of relay 320, this relay remaining operated, however, by virtue of the energization of its lower winding as described above.

At this point in the operation, the connection has been extended from the calling line to the central exchange and, as was mentioned previously, the steps following those described above necessary to a completion of the desired connection are dependent upon the type of equipment embodied in the central exchange. If this equipment is automatic in character, dial tone will be returned over the talking line conductors following the operation of the relay 320 indicating to the calling party that he may proceed to dial the desired line terminating in the central exchange. Operation of the dialing mechanism at the calling partys substation causes the line relay 2I0 to restore during each impulse of each digit, thereby opening the central oilice loop circuit at the armature 2I2 and causing the operation of a train of automatic switches such as selector and connector switches, whereby the called subscribers line is selected and signaled in the usual manner. The relays 3i@ and 320, due to their slow release characteristics, remain operated during the impulse transmission so that when the relay EIS energizes at the end of the final digit the talking loop is completed. Following the dialing, ringing current is supplied to the called subscribers line at the connector in use in the central exchange, this current being interrupted in the conventional manner, when the called party answers, by the operation of a ring cut-ofi relay.

From the foregoing description it will be apparent that in those systems wherein the central exchange includes automatic equipment associated with the trunk lines such as the line there is no necessity for applying ringing current to the conductors 23 and 24, since it serves no useful purpose. In the event manual equipment is employed, however, the ringing appara tus at the branch exchange may be used to apply ringing current to one of the line conductors 23 or 24 following the operation of the relay 328, to operate a signal at the central exchange, thereby to inform the operator in attendance to the trunk lines that a call is awaiting attention on the trunk line Alternatively, the signal means may be operated when ground is closed to the negative trunk line conductor at the armature 2|2 of relay 2|0, as described above. Whenv the operator answers the call, to receive the information necessary to a completion of the connection, the ringing current may be removed from the line conductor upon which it is impressed by any one of the several methods well known in the art.

Following the completion of the connection by either of the two methods described above, a talking loop is established between the calling and called lines which includes the trunk conductors 28 and 29, the armatures 23| and 232 of relay 230, the conductors 2| 4 and 2|5, the repeater 295, the armature 2|2 of relay 2li), the armatures 322 and 323 of relay 320 and the conductors 23 and 24 comprising the trunk line leading to the central exchange. It is pointed out here that only three relays and their interconnecting circuits are involved in setting up the connection through the repeater, namely the relays 2|0, 3|!! and 320. These relaysremain operated until the connection is cleared out.

Monitoring With the system in this condition, the operator at the attendants cabinet is aware that aY connection has been established over the trunk line due to the lighted condition of the busy lamp 400 and may monitor the call if desired by operating the trunk answer key 425 to the answer position to complete a circuit for operating the relay 220. This circuit extends from ground at the armature 43| of thetrunk connect key 426 by way of the contact 432, the conductor 444,

the contact 428 and the spring armature 402 of the switch 425, the conductor 404 and through the winding of relay 220 to battery. In response to the operation of the relay 220 the conductors 228 and 229 are respectively connected to the loop conductors 2|5 and 2|4 at the armatures 222 and 22|, respectively. The connection of Conductors 228 and 229 to opposite sides of the established talking loop extends the connection into the attendants cabinet and terminates the same at the terminals 465 and 466 of the operators telephone 50|).V Thus, the conductor 22B extends directly to the upper terminal 466, and the conductor 229 extends to the lower terminal 465 by a path including the armature 431 and contact 438 of the switch 421, the armature 44| and contact 442 of the switch 421, and the armature 434 and contact 433 of the switch 426, the terminal 465 being connected to Athe spring 453 and contact 452 of the impulsing device 458. As described previously, the potential across the lower winding 448 of the induction coil 450 is connected to the receiver 459 by way of the condenser 461 and the contacts 462 of the hook switch.

It may occur that the operator at the attendants cabinet will cut in to monitor a call before the connections for the call are fully established since the busy lamp 400 is lighted immediately upon operation of the relay 320. In order to prevent such action from interfering with the completion of the connections, there is provided in the conductor229 a condenser 485 in shunt with the contact springs 44| and 442 of the switch 421, which switch interrupts, when it is locked in its left-hand position, the direct current path through the induction coil windings 441 and 443. Thus, the operator, in order properly to monitor a call, should first operate the switch 421 to its left-hand locking position to cut thev condenser 485 into the circuit extending to the operators substation 500 and then operate the answer key switch 425 to its answer position to cause the operation of the relay 220 in the manner described above.

It will be noted that once the operator has cut in on an established connection to monitor a call the only way in which the apparatus can be released from the connection for further use is to restore the answer key 425 to its normal position, thereby -to open the energizing circuit of the relay 220. As will be pointed out hereinafter, not only is it possible to monitor a connection in the manner described above, but it is also possible to perform various other services such, for example, as the splitting of an established connection and the subsequent release o! Athe equipment for use in the completion of emergency calls.

Release The manner in which the established connection is released at the conclusion of the conversation held over the trunk line depends upon the nature of the equipment at the central exchange. If this equipment is automatic and when the party on the calling private line hangs up, the'bridge across the'talking conductors of the private exchange loop is removed, thereby interrupting the previously traced energizing circuit of the relay 2|0 and permitting it to restore to open at its armature 2|2 the central exchange talking loop and at itsarmature 2|| the energizing circuit of the relay 3|0. slow-torelease relay 3|0 restores after an interval opening: at its armature 3|| the holding circuit for the slow-to-release relay 320, at its armature 3|2 the connection to the ringing machine start conductor 221, at its armature 3|4 the ground connection to the C conductor 2|8, and closing at its armature 3|3 the winding of the relay 33D across the line conductors 23 and 24. Since the line relay equipment in the central exchange will normally, in response to the opening of the central exchange talking loop at the armature 2|2, remove battery from the conductors 23 and 24 before the slow-to-release relay 3|9 restores, the closure of armature 3|3 to the line conductor 24 does not result in the energization of the relay 330. Shortly thereafter the slow-to-release relay 320 restores, removing at its armature 32| the remaining ground connection to the C conductor 2 |8, thereby marking the trunk line as idle at the connector switch back contacts and extinguishing the busy lamp 400. At its armatures 322 and 323 the relay 328 prepares its initial energizing circuit and returns ground to the line conductor ex- Thek tending to the armature 2|2 of the relay 2|0, and at its X contacts open a further point in its holding circuit. The equipment is now in its normal or idle condition.

If, on the other hand, the central exchange equipment is manual in character, the trunk is held against seizure in the private exchange until the connection is cleared out at the central exchange, thereby guarding against a false routing of a subsequent call due to the seizure of the line before the prior connection is fully released. Thus, and with such equipment, battery is present across the line conductors 23 and 24 until the line is. cleared at the central exchange, so that, when the relay 3|!! restores and before the slowto-release relay 323 restores, the relay 330 is connected across the line at the armature 3|3 of relay 3m, and, at its armature 33|, closes an obvious energizing circuit for the relay 349. The latter relay immediately operates to close at its armature 34| ground to the holding circuit of the relay 32. These operations occur before the relay 320 releases so that this relay is held operated to maintain at its armature 232i ground on the C conductor 218, thereby to identify the trunk as busy at the connector bank contacts and to maintain the busy lamp 43@ lighted. When the central station operator clears the line atthe central exchange, battery is removed from across the line conductors 23 and 24, and the relays 330, and 343 restore, in the order named, to interrupt the holding circuit of the relay 323, whereupon the apparatus is restored to normal in the manner described above.

Calls from the central echange to the branch, exchange On an incoming call from a line in the central oice to a private line in the private exchange and following the seizure of the trunk line l l, battery is extended over the line conductors 23 and 24 to energize and cause the operation of the relay 330. This relay operates and at its armature 33| closes the energizing circuit of the relay 340. I'he relay 343 operates and; at its armature 34| prepares a holding circuit for the relay 320, at its armature 342 prepares a holding circuit for itself, at its armature 3M applies guarding ground to the C conductor 2 I 3, at its armature 345 closes an obvious energizing circuit for the relay 350, and at its armature 343 prepares a holding circuit for the slow-to-operate relay 31).

The relay 350 operates to close a holding circuit for itself at its armature 353 extending to ground at the armature 33| of the relay 330. This relay also closes ground to the ringing machine start conductor 221 at its armature 35|, completes, at its armature 352, a circuit for the lower winding of the relay 323, completes, at its armature 354, the branch circuit across the conductors 23 and 24 including the winding of the alternating current relay 36@ and the condenser 223, and prepares, at its armature 355, an energizing circuit for the winding of relay 243 by way of the conductors 2|1 and 236.

In response to the energization of its lower winding at the armature 352, the relay 326 operates to close multiple ground to its lower winding by way of the armatures 324 and 34|. In addition, this relay extends, at its armature 322, the line conductor 23 to the armature 2|2 of the relay 21'3, closes multiple ground to the C conductor 2| 8 at its armature 32| and removes ground from the positive line conductor 23 at its armature 323. Ringing current is now applied, in the usual manner, to the line conductors 23 and 24 at the central exchange, thereby causing the energiza.- tion and operation of the alternating current relay 368. This relay at its armature 36| completes, by way of the conductor 231, the energizing circuit for the relay 233. The latter relay at its armatures 23| and 232 connects direct generator to the line conductors 28 and 29 but without eiiect at this time, this current being effective only when the attendants cabinet apparatus is set to switch incoming calls by way of the li'ne conductors 234 and 265 to the night telephone in the manner to be described hereinafter. At its armature 234 the relay 233 connects over the conductor 233 a multiple ground to the winding of the relay 35i), and at its armature 233 completes an energizing circuit for the winding of the relay 3153, this circuit extending from ground at the armature 233, over the conductor 239 and through the winding of the relay 310 to battery.

. In response to the completion of its energizing circuit the relay 31B operates and at its armature 31| closes a locking circuit for itself which extends by way of this armature, the conductor 30| the armature 346, the conductor 302, the armature 242 and associated contact of the relay 240, the conductor 412, the contact M9 to ground at the contact spring 423 of the night kswitch 424. The relay 310 also completes at its armature 312 and associated front contact the energizing circuiti for the answer lamp 43|. 'I'his circuit extends from battery at rthe lower terminal of the relay 410 through the winding of the relay 410', the contact spring 499 of the switch 410, the conductor 412, the lamp 43E, the conductor 408, the armature 282 and associated contact of relay'280, and the conductor 26B to ground at the armature 312 and associated front contact of the relay 310. The answer lamp 43| and the busy lamp 430 are now both lighted, indicating to the operator that an incoming call from the central exchange-has been extended by way of the trunk line-1| to the private exchange and awaits her attention. The trunk line equipment is now conditioned for the extension of the connection to the desired private line by the operator. In this connection it is pointedout that following the completion of the ringing operation at the central exchangev the relay 36a restores to interrupt at its armature 36| the circuit of the relay 236.' As a consequence this latter relay restores to connect at its armatures 23| and 232 the line conductors 28 and 29, respectively, to the line conductors 2|5 and 2|4, respectively. Resto-ration of the relay 230 also opens at its armature 233 the original energizing circuit of the relay 312, and at its armature 234 opens the multiple ground circuits to the relays 343 and 350.

The Voperator or attendant answers the call by shifting the answer switch 425 associated with the trunk line ll from its normal to its off-normal trunk answer position to close the spring 42 to its associated contact 423 and thereby complete an energizing circuit for the relay 220, this circuit extending from ground at the armature 43| of the switch 426 by way of contact 432, conductor 444, spring 202, contact 428, answer conductor 43d and the winding of relay 220 to battery. Operation of the switch 425 to the answer position also prepares at the spring 403 and its associated contact 689 an energizing circuit for the relay 253, this circuit being held open at the contact spring 433 of the trunk conn-ect switch 426.

When the relay 220 operates in response, to its energlzation as above described, it pulls up its armatures 22| and 222 to connect the operators telephone set 500 across the conductors 2|4 and 2|5 by way of the conductors 228 and 229. This relay also completes at its armature 223 an energization circuit for the relay 240, which circuit extends from ground at the armature 223 over the conductor 236, the closed armature 355, the conductor 2|1 and through the winding of relay 240 to battery. The relay 220 also prepares at its armature 225 a path for connecting the 100 ohm resistor 261 across the conductors 25 and 21, this resistor being arranged to constitute a bridge across these conductors and functioning to cause operation of the line equipment at the selector switch 33' to prepare the local switch train of the private exchange to be responsive to transmitted dialing impulses. In addition, the relay 220 prepares, at its armature 224, a locking circuit for the relay 250.

When the relay 240 operates, it closes at its armature 24| a locking circuit for itself, which extends from this armature over the conductor 406 to ground at the spring 401 of the trunk switch 425. At its armature 249', the relay 240 completes obvious energizing circuits for the relay 3 0 and the upper winding of the relay 260. The relay 260 is, however, not operated at this time as the excitation supplied by the upper winding of this relay is insufficient to cause the operation thereof. The relay 240 also completes, at its armature 245, the talking loop extending from the operators telephone to the central exchange and at its armatures 244 and 246 prepares the normally uncompleted talking loop extending from the operators telephone by way of the line circuit comprising the conductors 25, 26 and 21 and the line switch- 33 to the called line. Operation of these armatures also connects the resistor 261 across the conductors 25 and 21 to cause the operation of the line switch 33 which results in the extension of the loop to a selector switch such as 20. The relay 240 also: disconnects, at its armatures 241 and 248, the winding terminals of the relay 2|0 from the line conductors 2|4 and 2|5; interrupts, at its armature 242, the previously-traced locking circuitI for the relay 310; removes, at its armature 249, the shunt from the condenser 218; and at its armature 243 closes an energizing circuit for the supervisory lamp 4|0, this latter circuit extending from ground at the armature 26| through the armature 243, over the conductor 401 and through the iilamentv of the lamp 4 0 to battery at the contact spring 4|| and associated contact of the switch 410.

When the relay 310 restores, it opens at its armature 31| a further point in its locking circuit and, at its armature 312 interrupts the previously-traced circuit of the answer lamp 40|, thus extinguishing the same. When theV relay 3 I 0 operates, in response to the completion of its energizing circuit at the armature 249', it immediately completes, at its armature 3|6, a multiple locking circuit for the relays 340 and 350, and at its armature 3|| completes a multiple lockingY circuit for the relay 320. At its armature 3|4, the relay 3| 0 closes multiple ground to the C conductor 2|8 and at its armature 3|5 it prepares a circuit for the energization of the relay 320. The relay 3|0 also closes, at its armature 3| 2, multiple ground to the ringing machine start conductor 221 and at its armature 3|3 removes the winding of the relay 330 from across the line conductors -23 and 24, permitting the latter relay to restore and open vthe original holding circuits for the relays 340 and 350. The latter relays remain operated, however, due to the completion of the previously-described multiple locking circuit extending from ground at the armature 3|6 of the relay 3|0.

With the equipment in this condition, a talking loop is established between the operators telephone and the central exchange, this loop extending from the terminals 465 and 466 over conductorsl 228 and 229, armatures 255 and 256, armatures 22| and 222 and conductors 2|4 and 2|5 to the windings of the repeater 200 from whence it extends over conductors 23 and 24 to the central exchange. The operator may now receive from the calling party or the operator in the central exchange the name or number of the desired party in` the private exchange. It ls pointed out here that the loop extending to the line switch 33 and the succeeding automatic switch train in the private exchange ls held isolated from the central exchange talking loop at the armatures 258 and 259 of relay 250 and at the armatures 212 and 213 of the relay 210, neither of these relays being operated at this time. It is further pointed out that the local switch train comprising the switches 33', 20, and

- I8 is prepared to respond to impulses transmitted from the impulsing device 458, since the closure of the resistor 261 across the lineconductors 25 and 21 upon the operation of the relay 220, caused the line switch 33 to operate and select an idle selector switch such as the switch for extending the loop to an idle connector in the proper group.

Following the receipt of the information necessary to the completion of the call and in order to render the impulsing device effective to cause the required operation of the automatic switches in the private exchange, the operator momentarily operates the self-restoring connect key switch 426 to close ground from the spring 435 to itsY associated contact 436, thereby to complete the energizing circuit for the relay 250. This circuit extends from ground at the contact spring 435 by way of the contact 436, the contact spring 403, the contact 409, the conductor 405, and through the winding of the relay 250 to battery. This relay operates immediately to close. at its armature the previously prepared locking circuit for itself and to disconnect, at its armatures 255 and 256, respectively, the central exchange loop from the conductors 228 and 229 leading to the operators telephone and to connect these conductors tothe conductors 25 and 21 leading to the line switch 33. It will be noted that the armatures 258 and 259 are actuated by the armatures 255 and 256, respectively, to disconnect the conductors 21 and 25, respectively, from the multiple conductorsr 216 and 211, respectively, leading to the armatures 213 and 212, respectively, so that the resistor 261 is removed from across the conductors 25 and 21, and the bridge comprising the operators substation is substituted therefor. In addition, the disconnection of the conductorsI 214 and 215 from the conductors 216 and 211, respectively, permits the relay 210 to operate, which it does before dialing, while maintaining the central exchange loop isolated from the loop to the line switch 33 over which the dialing impulses are transmitted. The relay` 250, at its armature 253, short circuits the condenser 218, thereby completing a metallic circuit to the line switch 33 for dialing, and at its armature 252 completes an obvious energizing circuit for the upper winding of the line relay 2 I0. At its' armature 251, the relay 250v prepares an obvious multiple locking circuit for the relay 240, this circuit being completed upon the operation of the relay 2 I Il and, at its armature 254, the relay 25) completes an energizing circuit for the relay 218, this latter circuit extending from ground on the control or C conductor 25, following the extension of the private exchange loop to the line switch 33 and the resulting operation of its associated equipment over the initiating circuit including the resistor 261.

When the relay 21B operates, it closes a locking circuit for itself at its armature 21I, prepares a locking circuit for the relay 280 at its armature 214, and at its armatures 212 and 213, furth-er prepares a loop circuit from the central exchange to the called line by way of the line switch 33.

In response to the energization of the upper winding of the relay 2li), this relay operates to close at its armature 2I2 a multiple loop circuit to the central exchange, to complete, at its armature 2I3, the previously prepared multiple locking circuit for the relay 24D, and to complete, at its armature 2l I, a multiple circuit for the relay 3|() and the upper winding of the relay 260. At this point the excitation supplied by the upper winding of this latter relay is insuiicient to cause operation thereof.

At this point the operators telephone is connected to the line equipment at the switch 33 over the loop circuit extending from th-e terminal 455, through contacts of the switches 426 and 421, the conductor 229, the armatures 255 and 258 of the relay 250, the conductor 214, the armature 245 of relay 240, the conductor 21, the windings of the line relay in series with battery at the line switch 33', the conductor 25, the armature 244 of relay 240, the conductor 215, the armatures 255 and 259 of relay 250 and over the conductor 228 to the terminal 456. The switch 33 then operates to connect the loop through to the rst selector. The operator now receives dial toneover this circuit which is applied thereto in the conventional manner in the local switch train of the private exchange.

The operator may now operate the impulsing device 458 to interrupt the loop circuit extending to the operated first selector in accordance with the digits dialed, thereby to cause the extension of the connection in the previously described manner to the line of the called party. If this line is busy, busy tone will be returned over the loop to the operator in a conventional manner and the operator may then inform the calling party to that effect and hold' the incoming call until the called line is idle or abandon thel call to disconnect thel trunk Il, depending upon the instructions received, all in the manner described in detail hereinafter.

If the called line is idle and the call is answered, the operator proceeds to complete the talking loop between the calling and called parties. This is accomplished by operating the answering key switch 325 to its normal position, thereby to remove, at the spring i552 and its associated contact 428, ground from the conductor 404 with the result that the energizing circuit for the relay 220 is interrupted and the armatures of this relay restore to their normal position. Operation of the key switch. 425 to its neutral position also interrupts, at the spring 203 and associated contact 599, the original and previously-traced energizing circuit for the relay 255` so that, when the relay 225 restoresto interrupt at its armature 224,' the `locking circuit for the relay 250, the latter relay also restores.

When the relay 220 restores, in addition to interrupting the lockingY circuit for the relay 250, it opens at its armatures 22! and 222 the circuit to the line conductors 2I4 and 2I5 for connecting these conductors to.` the conductors 228 and 229 leading to the operators telephone. In addition, the relay 225, at its armature 225, Opens an additional point in the bridging path across the conductors 2M and 2 I 5 and including the resistor 261. The relay 22@ also opens, at its armature 223, the previously-traced multiple locking circuit for the relay 240.

When the relay 252' restores in response to the interruption of its energizing circuit as described above, it opens a further point in its locking circuit at its armature 25E and, at its armatures 258 and 259, connects the central exchange loop to the private exchange loop, thereby to complete the talking loop between the calling and called lines. This relay also operates to open at its armatures 254 and 251, respectively, the original energizing circuit for the relay 216 and al further point in the previously-traced locking circuit for the relay 240. In addition, the relay 250 at its armature 252 opens the energizing circuit for the upper winding of the relay 2I0, thereby causing this relay to restore, but without effect at this time.

It will be seen that with the equipment in this condition the lower winding of the relay 25] is connected across the conductors of the talking loop extending to the called party line in series with the 500 ohm resistor 268. It will further be seen that the line conductors 228 and 229 extending to the operators telephone are disconnected from the talking loop at the armatures 22I and 222 of the relay 220.

When the called party answers by lifting his receiver from its hook, battery is reversed back over the loop circuit extending to the line conductors 2|!! and 2l5 in the conventional manner, so that, when the established private exchange loop is connected to the central exchange loop upon the operators restoration of the switch 425 to normal, the excitation furnished by the two windings of the relay 250 is cumulative and this relay operates. In response to its operation, an obvious energizing circuit for the relay 286 is completed at the armature 25I. With the same operation, ground is removed at this armature from the conductor 421 so that the previouslytraced energizing circuit for the supervisory lamp 4 I is interrupted and this lamp is extinguished to indicate to the operator that the proper operations have occurred to complete the loop between the calling and called lines. In addition, the relay 260, upon operating, at its armature 253, prepares a circuit including the armature 312 and the conductor 265 for energizing the answer lamp lIllI and, at its armature 262, vopens a point in an alternate energizing circuit for the saine lamp.

When the relay 280 operates, it closes the previously prepared locking circuit for itself at its armature 28| and closes its armature 282 to the associated back contact to prepare a circuit extending by way of the conductor 408 for the energization of the answer lamp 40 I.

With the system in this condition, all of the key switches at the operators station are in their neutral or normal positions and only the busy lamp 450 is illuminated to indicate that the trunk line II is being used. As regards the line equipment associated with ther trunk line I I and shown in Figslzands, th riays' i 10,220,130, 25u, ist; v

360 and 310 are restored and the remaining relays shown are in an operatedcondition. The talking loop established yby the operated relays 240, 260, 210, 280, 3|0, 320, 340, and 350 extends from the central exchange, over the trunk line comprising the conductors 23 and 24, through the repeater 200, and over the conductors 2 4, 2 5, 216, 211, 214, 215 to the line 35 comprising the conductors 25, 26 and 21.

Monitoring Ifrfor anyreason itis necessary or desirable to monitor the connection established in the manner described above, the operator may connect the telephone 500 to the line conductors 2|4 and 2|5 over which the transmission is taking place by operating the switch 425 to its left off-normal or answer position, thereby closing, over the conductor 404, the previously traced energizing circuit for the relay 220. Operation of this relay causes the line conductors 228 and 229 to be connected across the talking loop conductors at the armatures 222 and 22|, respectively. The operation of the remaining armatures of this relay has no effect at this time since the circuits in which they are individually included are either held open or multiplied at the armatures of certain ofthe other relays. With the equipment in this condition, the operator may listen to the ensuing conversation or break in on 'the conversation, as desired. It is pointed out that, with the system in this condition, the condenser 218 inserted in the conductor 229 is included in the circuit extending to the operators telephone as soon as the relay 250 is, as noted above, restored and the relay 240 is operated. The presence of this condenser prevents undue transmission loss between the calling and called substations. Restoration of the switch 425 to its normal position obviously opens the energizing circuit for the relay 220, permitting this relay to restore to its normal position thereby to open the monitoring connection.

Splitting the established connection It may for some reason be necessaryV for the operator to split a connection established'in the above-described manner and to connect her telephone to the called private line to the exclusion of the calling party. This may be accomplished by operating the switch 425 to the left off-normal or answer position to establish a monitoring connection, as described above, and thereafter operating the switch 426 momentarily to its right oflnormal position to close ground at the contact spring 435 of this switch to the conductor 405 and thereby complete the previously traced energizing circuit for the relay 250. This relay operates to complete a locking circuit for itself at its armature 25|, to close a shuntaround the condenser 218 at its armature 253, thereby completing a metallic bridge circuit through the operators telephone 500 for holding the local switch train operated, and to close at its armatures 255, 256 and 258, 259, the operators telephone to the talking loop extending to the called line. Operation of the armatures 258 and 259 also disconnects the last-mentioned talking loop from the central exchange talking loop so that the operator may talk withouteffect 'at this time; when the mop extending to the lower winding of relay 260 is opened in response to the operation of the relay 250, this relay restores, opening at its armature 26| the original energizing circuit for the relay 280 and completing at this same armature a circuit extending by way of the conductor 401 for energizing the supervisory lamp 4|0. The relay 280 is, however, maintained in its operated position by virtue of the completed holding circuit extending by way of its armature 28| and the armature 214' to ground.

' In order to re-complete the talking loop between the calling and called parties and to d sconnect the operators telephone from this loop, the operator actuates the answer switch 425 to its normal position, thereby opening at the contact spring 402 the previously traced energizing circuit for the relay 220 to permit this relay to restore. When the relay 220 restores, it opens the circuits holding the relays 250 and 2|0 operated, thereby permitting these latter relays to restore. When the relay 250 falls back, it re-completes the talking loop between the calling and called parties in a manner believed to be obvious from the preceding description, and when this loop is completed the relay 260 re-operates to open at its armature 26| the previously traced energizing circuit for thersupervisory lamp 4|0. The apparatus is now restored to the condition which prevailed before the extended talking loop between the calling and called parties was interrupted at the operators station.

Release of the connection by the private exchange operator When the conversation over the established connection is'terminated and the called party on the private line hangs up, battery is again reversed back over the talking loop extending from the calledline to the repeater 200, thereby differentially energizing the windings of the relay 260 and causingthis relay to restore. At its armature 26|, the relay 250V interrupts the original energizing circuit of the relay 280 and completes an energizing circuit, extending by way ofthe armature 243 and the conductor 401, for the supervisory lamp 4 0, this circuit being completed to battery at the spring 4| of the night alarm key switch' 410. The relay 280 does not restore in response to the restoration of the relay 260 since its energizing circuit is held completed over the locking path including the armature 28|. At its armature 262, the relay 260, upon restoring, completes'an energizing circuit for the answer lamp 40|, this circuit extending from battery through the winding of the relay 410', the spring 409 and associated contact of the key switch 410, the conductor 412, the filament of the lamp 40|, the conductor 408, the armature 282 of relay 280, the armature 262 of relay 260, and the conductor 269 to ground at the armature 312 of the relay 310. Thus, all of the lamps 400, 40| and 4|0 are illuminated, indicating to the operator that the trunk line and its associated equipment is now idle and may be released for further use.

The release of the equipment is initiated by momentarily operating the switch 425 to its right oir-normal or trunk release position, thereby to interrupt at its spring 401 and associated contact the holding circuit for the relay 240. This relay restores and at its armatures 244 and 246 opens the loop including the conductors 25 and 21 extending to the line equipment of the line switch 33', thereby initiating the release of the latter equipment in the usual manner. At its armature 245, the relay 240 upon restoring, opens the loop circuit extending by way of the conductors 23 and 24 constituting the trunk line II to the central exchange. The relay 24 also, upon restoring, opens at its armature 243 the previously traced energizing circuit for the supervisory lamp I0 and, at its armatures 241 and 248, reconnects the windings of the relay 2I|J across the line conductors 2I4 `and 2| 5. This latter operation is without effect, however, since at this time there is no bridge across the enumerated conductors 2|@ and 2I5. Restoration of the relay 248 also closes at the armature 242 a point in the locking circuit for the relay 310 and closes at the armature 24S a shunt around the condenser 218 included in series with the two halves of the conductor 229.

When, as above described', the line equipment at the line switch 33' is released, ground is removed from the C conductor 26 thereby interrupting the holding circuit for the relay 21B and causing this relay to restore. In response to the restoration of the relay 21D, a further point in its locking circuit is opened at the armature 21| and the holding circuit for the relay 280 is opened at the armature 211i so that this latter relay restores. Restoration of the armatures 212 andv 213, of the relay 210, to their respective normal positions has no effect at this time. When the relay 285 restores its armature 282, it interrupts the previously traced energizing circuit for the answer lamp 45|, causing this lamp to be extinguished and also opens, at its armature 28|, a

. further point in its own holding circuit.

In response to the restoration of the relay 24|), the relay 3|!) restores to reconnect at its armature 3 I3 the relay 33.!! across the line conductors 23 and 24. The latter relay operates, in the event the equipment at the central exchange has not cleared out, to close the holding circuit at its armature 33| for the relay 340, which latter relay closes, at its armature 34|, the holding circuit,

for the relay 32E? before this latter slow-to-release relay restores to remove ground at its armature 252i from the C conductor 2I8. The relay 33E) then retains ground on the C conductor 2|8 through the retention of the relays 320 and 340 in their respective operated positions, thereby mainy taining the trunk busy in the bank contacts of the connector switch in which the line comprising the conductors 28, 29 and 3U terminate. Vlhen the equipment at the central exchange associated with the trunk line I I is released, battery is removed from across the conductors 23 and 24 with the result that the relay 33|! restores to open at its armature 33| the holding circuit for the relay 320, permitting this relay to restore to normal. When the relay 34B restores, it opens at its armature 34|, the energizing circuit for the relay 222, which relay in turn restores and removes ground, at its armature 32|, from the C conductor 2 I8, thus marking the trunk line I I as idlein the bank contacts of the connector switches in which the line comprising conductors 28 to 30,

inclusive, terminate. All of the equipment associated with the trunk line II and illustrated in Figs. 2, 3, and 4 is now in its normal or idle condition, ready for further use.

' Transfer of operator telephone from private ea:-

change loop to central exchange loop by disconnecting the telephone B from the loop extending to the called line and connecting the same to the loop extending to the calling party, at the same time releasing the local switch train associated with the loop extending to the calledv line. This can be accomplished by momentarily operating the switch 426 to its left oi-normal position to interruptv at its contact spring 43| and the associated contact 432 the previously traced energizing circuit for the relay 22, thereby permitting this relay momentarily to restore to break atitsl armature 224 the established lockingY circuity forY the relay 250. All of the armatures of the. relay 220 necessarily restore but are reoperatedi in response to the reclosure of the energizing circuit for this relay at the contact 432 following the operators release of this non-locking switch 426 and its consequent restoration to normal. During the period of restoration of the relay 224.1, however, the relay 250 restores to further open at its armature 25| a point in its own locking circuit and consequently this relay remainsin. its restored position after the relay 220 is againoperated. With the equipment in this condition, the conductors 228 and 229 leading to the operators telephone 500 are connected to the conductors 2|5 and 214, respectively, included in. the loop extending to the central exchange, this connection comprising the armatures 256 and 255 and the armatures 222 andV 22|, As thus connected, the operator may converse with the calling party and receivev instructions as to whether the call should be held or the established connectionl should be released in the manner set forth above. Obviously when the relay 25@ restores, all of its armatures are restored, but without effect at this. time. If the calling party desires that the connection already established to the attendants cabinet not be held until such time as the called line is idle, the established connections as describedV above may be released in the previously described manner.

Hbldz'ng olf callsY at operators station If, however, the callin-g party desires that the call be held at the attendants cabinet until such time as. the called linev is idle, this may be acequipment in this condition, the busy lamp 4|l||V and the supervisory lamp 4|!) are lighted while the answer lamp 40| is extinguished, thus indicating to the operator that a call is being held on the trunk line II so that she may from time to time attempt to complete the desired connection or converse with the calling party as desired. In View of the foregoing description, the manner in which the operator may again connect her telephone to the linecomprising` the conductors 25 andV 21 extending to the line switch 33', to call the desired telephone, is believed to be obvious and is, therefore, omitted.

' In the event that the operator at the station forgets she is holding a call on the. trunk line II.

ecil

or if for any otherreason itis desired to signal the operator at the station |3 over a trunk line which is being held, this may be accomplished by the operator in the central exchange applying ringing current across the line conductors 23 and 24 of the trunk line to cause energization of the alternating current relay 360. When this relay operates, it closes its amature 36| to ground,v

to complete the energizing circuit for the relay 230. The latter relay at its armature 233 closes an energizing circuit 'for the relay 310, which relay in turn pulls up its armature 312 to complete, by way of the conductor 266, the armature 282 and the conductor 408, a circuit for illuminating the answer lamp 40|. Since the locking circuit for the relay 310 is, under the conditions stated, held open at the armature 242 of the energized relay 240, the relay 310 may periodically be energized in the above-described manner to ash the lamp 40| and attract the attention of the operator. By this method, a call is prevented from being held indenitely at the operators station due to the forgetfulness of the operator thereat.

' Called line is not answered In the event the called line is not answered following the initiation of a call thereto from the operators station,ringback tone is transmitted over the loop extending to the operators station, indicating to the operator the condition which prevails. Under these conditions, the operator may have instructions to call an alternative private line, or may believe that the called party may be reached by calling over another private line to another telephone in the same oifice, for example. In either case, and in order to establish the desired second connection, it is necessary that the local switch train be released without disconnecting the operators telephone 500 from. the loop extending to this switch train. It will be remembered that the condition of the apparatus is, under the circumstances stated, such that the switch 425 is in its left-hand oli-normal, or answer position and the relays 220 and 250 are, among others, operated. Obviously, it is desirable to release the local switch train without disturbing the operated condition of the two relays mentioned. This may be accomplished by momentarily operating the switch 421 to its righthand off-normal position to interrupt, at its contact springs 431 and 438, the metallic bridge circuit holding the local switch train operated and extending over the line conductors 228 and 229. Operation of the switch 421 to this position also closes the contact springs 439 and 440, but without effect since such closure merely completes a multiple energizing circuit for the relay 250 by way of the contact spring 403 of the switch 425 and 'conductor 405, this relay being already in its operated position. Interruption of the bridge circuit at the Contact springs 431 and 438 permits the line equipment at the selector switch 33 to initiate the restoration of the local switch train in a conventional manner. Following the momentary operation of the switch 421, the contacts 431 and 438 are again closed to recomplete the bridge circuit and thereby re-condition the local switch train to be responsive to dialing impulses transmitted from the impulsing device 458 at the operators station. The manner in which the operator establishes a talking loop through the local switch train to the second line is exactly the same as that described above in connection with the first called line and need not be repeated.

Night service As pointed out above, equipment is provided for the 'extension of calls from the central exchange directly to a predetermined part-y line during those periods when no operator is on duty at the operators station. This equipment includes the line conductors 264 and 265 connected respectively to the line conductors 28 and 29 and extending to contact springs in the night switch 424. In thev normal position of this switch, the conductors 264 and 265 are open circuited at their respective contact springs 422 and lM5. When, however, the attendant or operator is off duty, this key switch is locked operated in its oil-normal position to close its contacts 422, 423 and 4 4, 4| 5, thereby to extend the line conductors 264 and 265 to the line equipment of the predetermined substation designated for night service. Operation of this switch to its off-normal position also interrupts, at its contact spring 4|8, the energizing circuit for the answer lamp 400 and, at its contact 4|6, applies ground to the conductor 4 3 extending to the control conductor 2| 6, thereby to mark the trunk line as busy in the bank contacts of the selector switches to which conductors 28 to 30, inclusive, extend. At its contact 4|9, the switch 424 when operated toits off-normal position opens a point in the holding circuit `for the relay 310, this relay not being required for night service, since it performs only supervisory functions.

In addition to operating the night switch 424 to its oil-normal position, the operator may, if desired, operate the night alarm switch to its left oir-normal position where it locks, thereby preparing, at the contact springs 402 and 493, an energizing circuit for the buzzer or bell 494, this circuit being held open at the armature 41| of the relay 410.

When the night switch 424 is operated to its off-normal position in the manner described and when a call is initiated from the night telephone to the central exchange, the relay 2|0 is operated over the loop circuit comprising the conductors 2| 4 and 2|5 extending from the repeater 200 to the night telephone, which loop circuit is com.

pleted upon the night operators removal of his telephone set from its hook switch. The operation of the relay 2|0 initiates the sequential operation of the relays 3|0 and 320, in the order named, thereby extending the connection to the central exchange in a manner identical to that described above for calls to this exchange initiated on private lines in the branch oice. The release of this established connection is also eiected in the same manner as that described above for the type of call noted.

On an incoming call from the central exchange to the branch exchange by way of the trunk line and with' the night switch 424 and the night alarm switch 410 operated to their respective offnormal positions, the connection of battery across the conductors 23 and 24 energizes the relay 330, which relay in turn closes an energizing circuit for the relay 340 at its armature 33|. rI'ne relay 340, at its armature 345, completes an energizing circuit for the relay 350, which relay, at its armature 354, connects the winding of the alternating current relay 360 across the line conductors 23 and 24. The relay 350 also connects ground to the ringing machine start conductor at its armature 35|, completes an energizing circuit for the relay 320 at its armature 352 and completes a holding circuit for itself at its armature 353.

The relay r320 now operates to extend,y at its armature 322, the central oice loopy to the armature 2I2 of the relay 2H) and to disconnect, at its armature 323, ground from the positive line conductor 23. The relay 320 valso closes multiple ground to the control conductor 2I8 at its armature 32I and closes a locking circuit for itself at its X cont-acts and the armature 324.

When ringing current is applied to the con.- ductors 23 and 24 at the central exchange, the relay 36B energizes and, at its armature SGI, closes the energizing circuit comprising the conductor 231 for the relay 230. The latter relay operates to apply, at its armatures 23I and 232, directgenerator current to the conductors 264 and 255 leading to the night telephone and to complete, at its armature 233, an energizing circuit for the relay 310. The current from this generator energizes a signaling device at the night telephone indicating to the night operator that a call is to be answered. Operation of the relay 318 completes an energizing circuit for the ,relay 470', this circuit extending from ground at the armature 372 by way of the conductor 266, the armature 282, the conductor 4538, the lamp 49|, the Contact spring 489 through the winding of the relay lll'' to battery. When .the relay 416 operates it completes an obvious circuit for the signaling device 494. The device 434 continues to operate during such time as ringing current is applied to the conductors 23 and 24 to hold the chain of relays 350, 230, 310 and 410 operated. When ringing current is removed from the conductors 23 and 24, the relay 350 restores, thereby opening the energizing circuit of the relay '233 at its armature 36| and permitting the latter relay to restore. When the relay 230 restores, it interrupts the operation of the signal device 494 by causing the relays 3'IIl and 410 to restore, and returns its armatures 23| and 232 to the line conductors 2I4 and 2I5 extending to the repeater 2529, thereby further preparing the loop between the central exchange and the night telephone. When the night attendantv answers theV call by lifting his receiver from its hook, a bridge is connected across the conductors 264 and 285, completing over the loop comprising the conductors 254 and 265 a circuit for energizing the relay 2 I6. This relay operates and completes at its armature 2I2 the talking loop extending from the night telephone to the central exchange. Operation of the relay 2l!) also closes the previously traced energizing circuit for the relay 3Il3, which relay operates to disconnect, at its armature 3 I3, the winding of relay 330 from across the line conductors 23 and 24, thereby opening the original energizing circuit for the relay 34B. The latter relay is, however, held operated by a locking circuit extending to ground at the armature 353 of the relay 3l@ so that the connections as thus established are not disturbed.

When the conversation is terminated and the telephone at the night station is returned to its hook, the previously traced energizing circuit for the windings of relay 2H! is interrupted, permitting this relay to restore and cause the sequential restoration ofthe relays 3 I U, 340, 320 and 35i?, in the order named, providing, of course, the line equipment associated with the trunk line II in the central exchange has been cleared. If the call has not been cleared out at the central exchange, battery remains across the conductors 23 and 24, so that when the relay 3H! restores, the relay 33!) operates to close at its armature 331iy a holdlg circuit which maintains the relays 32,0, 340 and r35!) in their operated positions.l When the connection is cleared out at the central exchange, however, battery is removed from the conductors 23 and 24, permitting the restoration of the relay 330, followed by the restoration of the relays 340, 35) and 320, in the order named.

Secretarial or executive service As pointed out above, in addition to the service features already described, the arrangement includes lmeans whereby secretarial or executive service may be provided for at least predetermined ones of the private lines in the private exchange. Thus, an executive or other important oicial may desire to talk to a party whose location or telephone number is not immediately available. Y Under these circumstances, he may dial at his substation a predetermined digit known perhaps only to a few individuals, causing the selector switch Zllto extend the connection from thercalling line by way of the information trunkk line 3l directly to the loperators station. When this occurs, ground is lclosed at the selector switch 20 to theI control conductor vlll-J0, thereby completing an energizing circuit `for the information trunk lamp 484, which circuit extends through this lamp, the contact springr 409 and the winding of the relay 470', to battery. Illumination of the lamp 484 indicates to the operator that a call on the information trunk 3l is awaitingA attention,whereupon the switch 482 may be operated to its oi-normalnpositi'onkto form a talking loop between the telephoneV 500 and the calling telephone. Such operation of the switch 482 connects the operators telephone by way ofthe line conductors 445 and 4,46 to the line conductorsof the line 3l in an obvious man-y ner. The operation of this switch also closes ground to a second control conductor 49|, causing the operation of line equipment associated with the information trunk 3|, which results lin the interruption of the energizing circuit for the lamp 4814. Following the transmission of the desired information'to the operator, the calling party restores his telephone to its hook and the operator restores the switch 482 to normal, thereby releasingthe equipment involved and including the information trunk 3l and the operators telephone 50B.

If the operator believes that the desired party can be located at a telephone connected to one of the private lines, this line may be called without appropriating one of the central exchange trunk lines, such asthe line II, by means ofthe operators local switch 483 and associated line 32 extending by way of the line switch 33 to certain ones of the selector switches, such, for example, as the selector switch 20. Thus, the operator may call any desired private line by actuating the switch 433 to its cit-normal position to connect the substation 580 by way of the line conductors 445 and 445, the contacts of the switch 433 and the line 32 to the line switch 33. Closure of the substation bridge circuit across the conductors of the line 32 causes the line switch 33 to prepare the local switchtrain tobe responsive to dialing impulses, in the'k conventional manner.

-In this way the operator may by dialing the desired number establish a connection from the telephone Ellto the desired private line and, if the desired party is located, may communicate the name and number of the executivel Following this, .theestablished connection may be released by restoring. the switch 483 to its normal position' toinitiatethe releasefof the local switch train. Subsequently, the party receiving the information vmay Icall the executive in the manner previously described in connection with the description' of the :'system, generally, with particular reference Vto Fig. 1. From the immediately preceding description -it will be apparent that the operator may, by using the switch 483 and the equipment associated therewith, establish a connection to any of the lines in the private exchange without using the equipment associated with any of the central exchange trunk lines. Thisv feature `is desirable since the operators local calls,rwhich may constitute a large number, do not interfere with the regular use of the trunk lines and hence, in many instances, reduces the number of trunk lines required.

If`the party desired by the executive can only be reached over a connection by way of one of the central exchange trunk lines, the operator may connect the telephone 500 to an idle one of these lines, for example the line by operating the switch 425 to its left-hand off-normal o1' answer position, thereby to close the previously traced energizing circuit for the relay 220. This relay, upon operating, connects at its armatures 22| and 222 the operators substation 500 across the line conductors 2|4 and 2|5, thereby completing a metallic loop by way of the repeater windings and 202 for energizing the relay 2|0as described previously. This relay, upon operating, closes at its armature 2|| an obvious energizing circuit for the relay 3|0, which latter relay, upon operating, causes the operation of the relay 320 in a manner previously described and also disconnects, at its armature 3|3, the winding of the relay 330 from across the line conductors 23 and 24. When the relay 320 operates, it closes, at its armature 32|, ground to the C conductor 2|8, thereby marking the line as busy in the bank contacts of the selector switches and completing the previously traced energizing circuit for the busy lamp 400. This relay also completes, at its armatures 322 and 323, a talking loop from the operators substation to the central exchange and removes ground from the line conductor 24. The talking loop, as thus completed, may be ex tended to the desired line in the central exchange in the manner described in a preceding portion of the specification in connection with calls to the central exchange initiated on Vlines in the branch exchange. If the desired party is located, that `party may be instructed to hold the call while the operator recalls the executive in the private exchange. This latter operation is accomplished by actuating the switch 426 momentarily to its right off-normal position, thereby to close at its Contact springs 435 and 436 an energizing circuit for the relay 250. This relay operates to close, at its armature its holding circuit, to complete, at its armature 251, an energizing circuit for the relay 24|), to close, at its armature 252, a holding circuit for the relay 2|0, to close, at its armature 253, a shunt around the condenser 218, to prepare, at its armature 254, an energizing circuit for the relay 21D and to transfer at its armatures 255, 256, 258, 259 the operators telephone from the central exchange talking loop to the uncompleted loop extending to the called line. From this point on, the completion of the talking loop to the called line, the connection of this loop to the central exchange talking loop and the disconnection of the operators telephone from the last-mentioned loop are exactly the same as describedabove in connection with an 'incoming `call V'from the 'central "exchange toa private line in the branch exchange.

From the foregoing description, it will be apparent that, when the operatoris telephone 500 is disconnected from all lines and standing idle, all offthe operator controlled key switches are in their normal or restored positions. '.Conversely, when the operators substation 500 is connected to any one of the various talking loops described, the operator is aware of this fact not only by Virtue of the various audible signals transmitted to the receiver 459 as a consequence of such connection and by the condition of the signal lamps such as the lamps 400, 40|, 4||J and 484, but also by the position of the various key switches such, for example, as the switches 425, 482 and 483. Thus, in order to monitor an established connection in the manner described above, it is necessary that the switch 425 be locked in its left oir-normal or answer position and, further, that the lamps 400 and 4|0 be illuminated. As a consequence of this mode of operation, the possibility of mistakes on the part of the operator ls minimized, and it is practically impossible for any one of the central exchange trunk lines, such, for example, as the line to be tied up when it is in fact idle. It will further be noted that the Various types of services rendered are accomplished by the operation of a very small number of operator controlled switches, the various functions being concentrated in these switches to the greatest extent. Thus, the means for preparing the local switch train in the central exchange to be responsive to dialing impulses transmitted from the operators substation 500, for establishing a talking loop between the central exchange and a telephone in the private exchange, for monitoring such a connection, and for releasing such a connection are individually responsive to the operation of the switch 425 to predetermined positions. Again, the means for transferring the operators telephone from an established central exchange talking loop to a previously prepared but uncompleted private exchange talking loop and for restoring the operators telephone to a connection with the central exchange loop and simultaneously initiating the release of the established local switch train associated with the private exchange talking loop, are individually both responsive to the momentary operation of the switch 426 to predetermined positions. Finally, the means for releasing the local switch train associated with an established connection between one of the private lines and the operators telephone without disconnecting the operators telephone from the restored private exchange loop and thereafter re-preparing the switch train to be responsive to dialing from the operators telephone, and for simultaneously splitting an established connection between a private exchange loop and a central exchange loop, releasing the local switch train holding the loop extended to the called private lines and connecting the operators telephone across the line conductors extending to the local switch train are individually responsive to the momentary operation of the switch 421 to predetermined positions. These Various means include means comprising the two relays 22B and 250, which relays are directly responsive to the operation of one or more of the switches noted to one or more predetermined positions. 'Ihis feature of concentrating the switch operations in a few relay controlled switches and of connecting the relays to perform the actual switching operations, results in a very simple circuit arrangement while retaining the ilexibility of operation. normally found only in more complicated systems.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will beapparent that various modifications may be made therein, and it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said lines having private telephones individually associated therewith, an operators station, an operators telephone at said station, means for establishing a talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said telephones, an operator controlled switch at said operators station, means operative in response to the momentary operation of said switch to a predetermined position for initiating or completing a predetermined service in connection with calls extending over said trunk line and means independent of said switch for retaining said last-mentioned means operated.

2. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible toV said trunk line, at least a portion of said lines having private telephones individually associated therewith, an operators station, an operators telephone at said station, means for establishing a talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said telephones, an operator controlled switch at said operators station, said switch having a normal position and at least one oli-normal position, means operative in responseY to the momentary operation of said switch to a predetermined off-normal position for initiating or completing a predetermined service in connection with calls extending over said trunk line, and means independent of said switch for retaining said last-mentioned means operated.

3. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said lines having private telephones individually associated therewith, an operators station, an operators telephone at said station, means for establishing a' talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said telephones, an operator controlled switch ,at said operators station, means including at least one relay associated with said trunk line and operative in response to the momentary operation of said switch to a predetermined position for initiating or completing a predetermined service in connection with calls extending over said trunk line, and means independent of said switch for retaining said relay operated.

4. In a telephone system, a central exchange, a private exchange, a trunk line extending loetween said exchanges, private lines in said private exchange and accessible to said trunk line, at least 1 5 a portion of said private lines having private telephones individually associated therewith, lan operators station, an operators telephone at said station, means for establishing a talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said private telephones, a plurality of operator-controlled switches at said operators station, means individually operative in response to rthe momentary operation of certain ones of said switches to predetermined positions for rendering predetermined services in connection with calls extending over said trunk line, and means independent of said switches for retaining said lastmentioned means operated.

5. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said private lines having `private telephones individually associated therewith, an operators station, an operators telephone at said station, means for establishing a talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said private telephones, a plurality of operator controlled switches at said operators station, and means independent of said switches and individually responsive to the momentary operation of certain ones of said switches to predetermined positions for rendering predetermined services in connection with calls extending over said trunk line.

-6. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said private lines having private telephones individually associated therewith, an operators station, an operators telephone at said station, means for establishing a talking loop between one of said private telephones and said central exchange, said loop extending by way of said trunk line and the line associated with said one of said private telephones, a plurality of operator-controlled switches at said operators station, and means including a plurality of relays associated with said trunk line and individually responsive to the momentary operation of certain ones of said switches to predetermined positions for rendering. predetermined services in connection with calls extending over said trunk line.

'7. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said private lines having private telephones individually associated therewith, an operators station; operator-controlled switches at said station individually having a normal position .and being operable to at least one off-normal position, means including means responsive to the operation of one of said switches to a predetermined off-normal position for preparing a talking loop between one of said private telephones and said central exchange by way of said trunk line on a call to said private exchange routed over said trunk line, means responsive to the operation of said one of said switches to its normal position for completing said loop, and means responsive 4to the operation of another of saidswitches to a predetermined off-normal position for perform- ,ing a predetermined service in connection with callsextending over said trunk line.

8. In a telephone system, a centralexchange,

a private exchange, a trunk line extending'between said exchanges, private'lines in said private exchange and accessible to said trunk line, at least a portion of said private lines having private telephones individually associated therewith, an-operators station, operator-controlled switches at said station individuallyhaving a normal position and being operable to at least one off-normal position-means including means responsive to the operation of one of said switches to a` predetermined off-normal position for preparing a talking loop between one of said private telephones and said central exchange by way of said trunk line on a call to said private exchange routed over said trunk line, means responsive to the operation of said one of said switches toits normal position for completing said loop, and means responsive to the momentary operation of another of said switches to a predetermined ofinormal position forpe-rforming a predetermined service in connection with calls e-xtending over said trunk line. Y

9. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible tosaid trunk line, at least a portion of said private lines having private telephones individually associated therewith, an operators station operator-controlled switches at said station'individually having Ya normal position and being operable to at least one orf-normal position, means including means responsive to the operation ci one of said switches to a .predetermined off-normal position for preparing a talking loop between one of said private telephones and said central'exchange by way of said trunk line on a call to said private exchange routed over said trunk line, means'responsiveto the operation of said one of said switches to its normal position for completing said loop,` and means responsive to the operation'o another of said switches to a predetermined off-normal position for performing a predetermined service as regards the established talking connection comprising said loop.

1.0. In a telephone system, a central` exchange, a private exchange, a trunk linel extending-between said exchanges, private lines lin said private exchange and accessib-le to said trunk line, at least a portioncf said private lines having private telephones individually associated therewith, an operators station, operator-controlled switches at said station individually having a normal position and being operable to at least one off-normal position, means including means responsive to the operation of one of said switches to a predetermined ofi-normal position for preparing a talking loop between one oi said private telephones and said central exchange by way of said trunk line on a call to said private exchange routed over said trunk line, means responsive to the operation of said one of said switches to its normal position for completing said loop, means responsive to the operation of another of said switches to a predetermined oif` normal position for performing a predetermined service in connection with calls extending over said trunk line, and means including means responsive to the operation of said one of said switches to a second off-normal position for releasing the established connection comp/rising saidV talking loop. Y f

11."In a'telephone system,'a central exchange, aprivate exchange, a trunk line extending between said exchanges, priva-te lines in said private exchange `and accessible to said trunk line, at least a portion of said private lines having private-telephones individually associated therewith, an operators station, operator-controlled switches at said station individually having a normal position and being operable to at least one off-normal position, means including means responsive to the operation of one of said switches to a predetermined off-normal position for preparing a talking loop between one of said private telephones and said central exchange by way of said trunk line on a call to said private exchange routed over said trunk line, means responsive to the operation of said one of said switches to its normal position for completing said loop, means responsive to the operation of another of said switches to a predetermined off-normal position for performing a predetermined service in connection with calls extending over said trunk line, and means including means responsive to the momentary operation of said one of said switches to a second off-normal position for releasing the established connection comprising said talking loop.

12. In a telephone system, a central exchange, a private exchange, a trunk line extending between said exchanges, private lines in said private exchange and accessible to said trunk line, at least a portion of said private lines having private telephones individually associated therewith, an operators station, operator-controlled switches at said station individually having a normal position and being operable to at least one olf-normal position, means includingmeans responsive to the operation of one of said switches to a predeterminedo-normal position for preparing a talking loop betweenk one of said private telephones and said central exchange by way of said trunk line on a call to said priva exchange routed over said trunkV line, meansresponsive to the operation of saidone ofsaid switches to its normal position for completing said loop, means responsive tothe momentary operation of another of said switches to a predetermined off-normal position for performing a. predetermined service in connection withfcalls extending over said trunk line, and means including means responsive. to the momentary operation of said onev ofV said switches to a second off-normal position for releasing the established connectioncomprising said talking loop. f

13. In a telephonesystem, -a central exchange, a `private exchange, a trunk-line extending between said exchanges, private lines in said private exchangev and accessible to said trunk line, at least a portion of said lines having private telephones individually associated therewith, an operators station, an-operators telephone -at said station, an operator-controlled switch at said station, means including means responsive to the operation of said switch to a predetermined position for completing a talking loop from said operators telephone toone of said private lines on a call from said central exchange routed over said trunk line to'said one of said private lines, and means responsive to the momentary operation of said switch to another position Vfor interrupting said talking loop and for completing a talking loop extending from said operators telephone over said trunk line Vto said central exchange.

14. Ina telephone system, a central exchange, a private exchange; a trunk line extending be- 

